Wave guide attenuator



Oct. 7, 1952 P. B. KING, JR 2,613,270

WAVE GUIDE ATTENUATOR Filed May 24, 1946 Patented Oct. 7, 1952 s PATENT OFFICE I WAVE GUIDE ATTENUATOR .Paul B. Kingpin, Mountain Lakes, N. J assignor to, AircraftRadio Corporation, Boonton, N. J., a corporation of New Jersey T Application May- 24, 1946, Serial No. 671,950

g g i Q; is-cl ms. (01. 178-44) i This invention relates to waveguides and more particularly to adjustable attenuators fonwave guides, ILL].

' Theprior adjustable attenuators have usually been of a cam and lever type, the lever carrying a strip of semi-conductive material .whichl was projected into the wave guide tosa greater orv less extent by the angular adjustment of the. cam. The operating characteristics of such. attenuators were far from satisfactory as it was difiicult or impossible to meet the several requirements of long range attenuation, adequate shielding, stable calibration and. ease of adjustment to a desired value.

- Objects of the invention are to provide-wave guide attenuators which may be. accurately adjusted to preselected values by the use of graduated dials and which,'if desired, may be of long range and/or completely shielded. An object is to provide rotary attenuators for wave guides, the attenuator element being a non-circular disk or a varying-diameter arcuate strip which is introduced to a greater or less .extent into the wave guide upon angular adjustment, of, a shaft which carries the attenuator'element. An object is to provide an attenuator includinga rotatable shaft carrying-.a cam strip of semi-conductive material extending radially therefrom, thesection of the wave guide into which the strip may be projected by angularadjustment of the'rotatable'disk being curved and concentric, orsubstantially .concentric, with the rotatable disk.

These and other objects and advantages of the invention will. be apparent from the following specification when taken with the accompanying drawings in which: A V "I Fig. 1 is aside or. edge elevation of a rotary attenuator embodying the invention;

Figs. 2 and 3 are-inside elevations of the cover plate .and the back plate, respectively, of the wave guide and attenuator casing; M

4 is a vertical central section but with someiparts in partial elevation, through the rotary attenuator;

- Fig.4a is a fragmentary vertical section, on a greatly enlarged scale, of an edge portion of the attenuator element and its supporting disks; Fig.5 is an inside elevation, on the same scale as Fig. 4, of the cover plate with the attenuator mounted thereon;

Fig. 6 is a verticalsection through another embodiment of the invention; and

' Fig. 7 is a partly sectional view of the same as seen from the inner face of the cover plate.

In the drawings, the reference numerals band 2 identify the cover plate and the back plate, re"- spectively, ofa wave guide and attenuator casing of the split plate type which is described and claimed in my copending application SerialNumber 671,949 filed May 24, 1946, now Patent No. 2,574,790, granted November 13, 1951. Y

Complementary grooves 3, 4 in the plates l ,-2 respectively cooperate to form a wave guide-of rectangular cross-section when the plates are assembled, the wave guide passage being ofsemi circular shape between straightend sections which extend toopposite edges of the casing I,- 2 where connections are made to'tubular wave guides 5, 5. The plates are clamped to each other after the attenuator assembly is mounted on the front plate 1, and the clamping devices are preferably designed for an accurate relative positioning of the plates to insure the alinement of the cooperating grooves 3, 4 of the wave guide path within the attenuator casing. As illustrated in Figs. 2 and 3, the cover plate I has'steel studs secured thereto which have a snug fit in open ings l' of the plate 2, the studs having threaded bores which receive the clamping screws 8. The plates 1, 2 are recessed at their inner faces, as will be described later, to receive the attenuator assembly.

The attenuator elementis an arcuatestrip 9 located in substantiallythe median plane of the wave guide formed by the grooves 3, 4, and supported for angular adjustment about the axis of the arcuate section'of the wave guide to project to a greater or less extent into the wave guide. As best shown in Figs. l and 4a, the attenuator strip 9 is clamped between annular disks [0, II by a series of screws l2, and the assembly is secured to and supported by a rotatable shaft [3. The flared inner end of the shaft [3 forms a seat for the outer face of the disk I0, and the end M of the shaft 13 is spun over the inner face of the disk I!) and staked at a plurality of points It to project into slots iii of the disk I0 to lock the parts against relative angular movement. The shaft 13 is journalled in a hub l5 and, preferably, a ball bearing 66 is arranged between the inner endsof the shafts I3 and the hub 15. A collar I7 is pinned to the shaft 13 outside of the hub I5, and a spring washer I8 is arranged between the collar I? and hub [5 to eliminate end play of the shaft in the hub. A knob may be mounted on the shaft l3 for a direct manual adjustment of the attenuator but itis preferable to secure a pinion l9 on the shaft I3 and to drive the pinion through any desired type of reduction gearing, not shown, to obtain a fine and accurate adjustment of the attenuator. A graduated dial, not shown, may be mounted on the shaft I3 or upon a shaft of the gear train.

The hub l5 has a, radial flange 28 at its inner end for seating against the recessed inside face of the plate I, and one or morepins 2% project forwardly from the flange 2G to seat in cooperating sockets of the plate, thereby locking the hub l5 against rotation. The hub section 21 in front of flange 20 is of somewhat reduced diameter and threaded to receive a gland nut 22 which secures the attenuator assembly'to the plate i.

Reverting to the construction of the plates I, 2 which provide a housing for the attenuator assembly, the plates I, 2 have circular recesses 23, 24 for receiving the disks In, II respectively, and shallow arcuate recesses 25, 26 complementary to the arcuate sections of the wave guide grooves 3, 4, and of the same outer diameter, to. receive the attenuator strip 9 when it is rotated to clear the wave guide. The circular recesses 23 and 24 are somewhat larger than the disks l and II and are lined with rings 21 and 28- of highly lossy material such as powdered iron bonded by an insulating plastic. The purpose of the rings is to prevent energy from leaking across the chord of the shaped waveguide, which might give rise to undesirable attenuation characteristics such as a dependence of attenuation on frequency. Rings 2! and 28 also prevent energy from leaking from the waveguide into external space.

The contour and the composition of the attenuator strip 9 may be selectedto obtain any desired relation between the attenuation and the angular adjustment of the attenuator strip. The outer edge of the strip 9 may be circular or non-circular, and the strip 9 may be of semiconductive material of a lossy dielectric type, for example a thin sheet of a molded plastic containing or coated with carbon or a metallic powder. The conductive material may be uniformly distributed upon or throughout the plastic strip or it may be graduated along the strip.

As illustrated, the attenuator strip 9 is a thin sheet or plastic coated on its inner face with a thin layer 9 of conductive material. The conductive layer 9' may be formed by sputtering a metal upon the plastic strip 9 or by painting the strip with a graphite suspension such as that sold under the trade-mark, Aquadag. The desired attenuation characteristic is readily attained by initially providing an excess of conductive material in or upon the surface of the strip 9 and then scraping away the edge a of the strip 9 to remove sufficient conductive material to reduce the effective attenuation to specified limits.

The shaft [3 may be continuously adjustable for a progressive variation of the attenuation, or it may be adjustable between alternative end positions corresponding to maximum and minimum attenuation respectively. A number of attenuators may be incorporated in a single wave guide assembly of the split plate type which is provided with a plurality of sets of complementary grooves forming a more or less complex wave guide pattern. A typical multiple-branch wave guide system in which a plurality of rotary attenuators are to be incorporated is illustrated in Figs. 5 and 6 of my copending application.

It is usually preferable to form the wave guide in the complementary plates I ,2 within which the attenuator is mounted but it is also possible, as will appear hereinafter, to employ a tubular wave guide of arcuate contour which fits snugly within or against the corresponding curved edges of the complementary plates which house the rotary attenuator.

The construction may be materially simplified when the design requirements do not necessitate a fine adjustment of the attenuation over a. long range or do not necessitate maximum shielding.

As shown in Figs. 6 and 7, a cam shaped attenuator disk 29 is secured to the end of a shaft 30 by an end disk 3| and screws 32. The shaft is journalled in a plate 33 and secured thereto by a spring clip 34, and the shaft may be adjusted angularly by any desired mechanism which is shown schematically as a knob 35. A complementary back plate 36 is secured to the plate 33 by screws 31, and the plates are grooved to form a wave guide passage or, as illustrated, to fit over a tubular wave guide 38 which is slotted to permit the projection of the attenuator disk 29 into the wave guide.

As indicated above, this type of clamped-on attenuator assembly may be employed in the manufacture of the more elaborate attenuators such as shown in Figs. Ito 5.

It is to be understood that the invention is not limited to the particular embodiments herein shown and described as various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

I claim: 1

1. In a wave guide of adjustable transmission characteristics, means defining a wave guide passage having a slot at its transverse medial plane, an arcuate attenuator element, and means supporting said attenuator element for rotary mo-- tion to project the same through said slot to enter the wave guide passage, said supporting means comprising a pair of complementary plates with recessed inner faces between which said attenuator strip is located. I

2. In a wave guide of adjustable transmission characteristics, the invention as recited in claim 1 wherein said plates have complementary mating grooves forming said wave guide passage.

3. In a wave guide of adjustable transmission characteristics, the invention as recited in claim 1 wherein said plates have complementary grooves in which is seated'said means defining a wave guide passage.

4. In a wave guide attenuator, a pair of complementary plates in face contact and having mating transverse surfaces adapted to seat against a longitudinally sloted wave guide tube; said plates having complementary cylindrical recesses open at said transverse surfaces, an attenuator element having an arcuate outer edge, and means rotatably supporting said attenuator element in said recesses for rotary movement to project said outer edge beyond said transverse surfaces and to withdraw the same into said recesses.

5. In a wave guide attenuator, a pair of complementary plates in face contact, the inner faces of said plates having complementary grooves defining a wave guide passage and having cylindrical recesses opening into said wave guide passage, an attenuator element, and means supporting said attenuator element in said recesses for rotary movement into and out of said wave v guide passage.

6. In a wave guide attenuator, the invention as recited in claim 5, wherein said attenuator element is an arcuate strip projecting beyond and secured between a pair of annular disks, said disks being located in said cylindrical recesses.

7. In a wave guide attenuator, the invention as recited in claim 5, wherein said attenuator element is an arcuate strip projecting beyond and secured between a pair of annular disks, said disks being located in said cylindrical recesses, and, said supporting means includes said disks and a shaft secured thereto, said shaft projecting through one of said plates and carrying means for angularly adjusting the same.

8. In a wave guide attenuator, the invention as recited in claim 5, wherein said wave guide passage includes a section of arcuate contour substantially coaxial with said cylindrical recesses, and said attenuator element is an arcuate strip having an angular length substantially equal to the angular length of the arcuate contour section of said wave guide passage.

9. In a wave guide attenuator, the invention as recited in claim 5, wherein shielding means is located at the periphery of said cylindrical recesses.

10. In a wave guide attenuator, the invention as recited in claim 5, wherein rings of ferroma netic material are located at the periphery of said cylindrical recesses.

11. In a wave guide attenuator, the invention as recited in claim 5, wherein rings of powdered iron in an insulating binder are located at the periphery of said cylindrical recesses.

12. In a wave guide attenuator, the invention as recited in claim 5, wherein said attenuator element comprises a cam shaped disk.

13. A variable attenuator for electromagnetic waves comprising a hollow wave guide formed into the arc of a circle and having a longitudinal slot in the concave side thereof and an arc of resistive material having a greater radius than said slot mounted for rotation about the center of said circle so that said element can be introduced into said guide through said slot.

14. An attenuator in accordance with claim 13 which includes means for indicating the position of said are of resistive material within said guide.

15. An attenuator in accordance with claim 13 in which said guide is formed into a semicircle and is of rectangular cross section with unequal cross-sectional dimensions, said slot is centrally located in one of the wider sides of said guide, and said arc of resistive material gradually decreases in radius at one end.

PAUL B. KING, J R.

No references cited. 

